Acer E1-531 Motherboard LA-8331P No Display

[beogeek]

Hi Folks,

So I have an Acer E1-531 Motherboard LA-8331P with No Display. The laptop runs fine via HDMI and VGA but no picture for the LCD display.

I have the schematics and board view files, I first suspected that the previous "repair shop" disconnect the LVDS connector with the battery connected, so I started with the basics. I checked the LVDS cable, it's fine. I check the inverter on the display and that's fine too. I suspected the super IO was damaged, so I replaced it and re-programmed it, I also reflashed the BIOS, and yet still no display.

So I got a known-good display and yet the same issue so I know it's not the display, it's not the super IO, it's not the LVDS cable and it's not the BIOS!

After checking some of the voltages around the N channel MOSFETs that create the power signal for the screen to turn on are missing. I can see that the DP_INT_PWM that comes directly from the CPU is missing, thus so are some other lines because this one is missing.

My question is this... Can it really be the CPU that's causing the no display to be shown on the LCD even though everything else is functioning fine?!?!

If anyone requires the schematic or board view file I will be happy to post it if that is permitted. Cheers and I look forward to hearing your opinions!

[mon2]

Re: Acer E1-531 Motherboard LA-8331P No Display

hi. see schematics on this forum but unable to locate the boardview files.

Perhaps you can update the following thread with your schematic (if different than the one that is posted) & boardview files?

https://www.badcaps.net/forum/showth...light=LA-8331P

[beogeek]

Re: Acer E1-531 Motherboard LA-8331P No Display

Done, updated the original thread, and uploaded my board view file, the schematic is the same as the original posted here https://www.badcaps.net/forum/showth...light=LA-8331P

[mon2]

Re: Acer E1-531 Motherboard LA-8331P No Display

1) voltage @ +LCDVDD with the lcd attached ? (configure to use the display for these measurements)

2) voltage @ Q28B (pin # 5)

3) voltage @ DISPOFF#

4) voltage @ EDP_HPD?

5) voltage @ I2CC_SCL ? I2CC_SDA ?

[beogeek]

Re: Acer E1-531 Motherboard LA-8331P No Display

1) voltage @ +LCDVDD with the lcd attached ? (configure to use the display for these measurements) 3.276 Yes display is attached

2) voltage @ Q28B (pin # 5) 3.172 (I only have Q28 not Q28B)

3) voltage @ DISPOFF# 0

4) voltage @ EDP_HPD? 0

5) voltage @ I2CC_SCL3.172 ? I2CC_SDA 3.322?

[mon2]

Re: Acer E1-531 Motherboard LA-8331P No Display

voltage @ DISPOFF# 0

From the '#' suffix in the label name, this is an active low signal so the signal is requesting the LCD display to remain OFF (or the signal is not used).

Do you have the parts on your logic board that are driving the DISPOFF# line such as:

U22 dual input AND gate ?

I believe that the '@' symbol is used to denote parts that are NOT stuffed on the PCBA. Confirm if R730 is the only pull-down resistor on this line.

[beogeek]

Re: Acer E1-531 Motherboard LA-8331P No Display

Yes R730 is present, but my board does not have U22

[beogeek]

Re: Acer E1-531 Motherboard LA-8331P No Display

So I've tested the following also.

PU19 PIN 3 is 3.3v which goes into PR275 at 3.3v which goes to Q51 at which point on pin 1 of Q51 there's 0v then it goes to R1097 pin 1 is 0v and pin 2 is 5v

At R637 and R638 there's 0v on both of them. Q21 pin 2 is connected to R637 and there's 0v on pin 1 of Q21 there's 3.3, Q21 goes to pin 2 of Q20 and there's 3.3v but on pin 1 of Q20 there's 0v

This is why I suspected that the CPU is the issue but I may be wrong...

[mon2]

Re: Acer E1-531 Motherboard LA-8331P No Display

But if the laptop works fine with HDMI and VGA then cpu I believe is working ok.

Review if there is the RTD2132S @ U46 onboard. It is the eDP to LVDS bridge. Confirm the components are present to power this bridge and that the lvds signals are reaching the lvds screen connector.

Perhaps the RTD2132 is defective. It is inexpensive on AliExpress.

Any chance you have the datasheet for the RTD2132S?

[beogeek]

Re: Acer E1-531 Motherboard LA-8331P No Display

Nope, I don't have the RTD2132S on my board...

[mon2]

Re: Acer E1-531 Motherboard LA-8331P No Display

Q51 is a mosfet based logic inverter.

The way the schematic is drawn it appears the EC is monitoring the VLDT_EN line. I think that it may be driving the line.

Perhaps the EC needs to be reflashed. Personally do not have experience with this topic but will be reflashing the EC of an Asus mb very soon. Stuck with too much ground plane to desolder an external soic flash device.

I believe the KB9012 (U31) is with an internal flash.

Consider it and keep this thread posted.

[beogeek]

Re: Acer E1-531 Motherboard LA-8331P No Display

haha yes, I've already done that, have reflashed the EC but still the same issue. NOW I did backup the original and then soldered on a new KB9012 and flashed it using the original data from original the EC! Maybe that could be the cause as I know that the new KB9012 is fine and working ok. I will try finding a dump and seeing if reflashing will help. But thanks for coming to a similar conclusion yay I'm not dumb or going crazy!

[mon2]

Re: Acer E1-531 Motherboard LA-8331P No Display

Wait...can the lvds display even function without the RTD2132S bridge?? Maybe it was removed by another tech?

[beogeek]

Re: Acer E1-531 Motherboard LA-8331P No Display

I just checked again under the microscope and no it doesn't appear it was ever on the board as if it was there would be traces of work around it, what I'm trying to say is that it looks factory that U46 (RTD2132S) is missing...

[mon2]

Re: Acer E1-531 Motherboard LA-8331P No Display

Not familiar with this topic but it appears from page 2 of the schematic that at build time...

LVDs display can be used if RTD2132S bridge is on-board.

Or

eDP panel must be used if the bridge is missing.

Can you confirm that your display being tested is eDP interface?

[beogeek]

Re: Acer E1-531 Motherboard LA-8331P No Display

how do I check if the display is or has a eDP interface? On the back of the display?

[mon2]

Re: Acer E1-531 Motherboard LA-8331P No Display

I would review any and all labels and try to find the datasheet to review the connector pinout. Review the eDP signals on the common lcd display connector and see if it mates properly for the logic board. You can see the eDP labels on some pins.

Is the display the original for this laptop or is it a replacement?

Post the display markings here when you can. It HAS to be late for you or you have had too much caffeine? 😁

Going to watch another episode of Fauda..will check for your post later today or tomorrow.

[mon2]

Re: Acer E1-531 Motherboard LA-8331P No Display

https://www.laptop-lcd-screen.co.uk/...N%20connectors.

[beogeek]

Re: Acer E1-531 Motherboard LA-8331P No Display

I would review any and all labels and try to find the datasheet to review the connector pinout. Review the eDP signals on the common lcd display connector and see if it mates properly for the logic board. You can see the eDP labels on some pins.

Is the display the original for this laptop or is it a replacement?

Post the display markings here when you can. It HAS to be late for you or you have had too much caffeine? 😁

Going to watch another episode of Fauda..will check for your post later today or tomorrow.

Yes I have the original display and a replacement and they both use a 40 pin LVDS connector. Both LVDS cables are the same, including the original that was with the laptop...

Yea it is late almost 3AM... I better go and start again tomorrow with a fresh pair of eyes. I'll update the thread tomorrow. Thanks for the helping hand, it's much appreciated!

[beogeek]

Re: Acer E1-531 Motherboard LA-8331P No Display

So this has turned into a nightmare, this is precisely why I hate working on machines someone else has tinkered with!

First I'd like to thank @mon2 for the help, it led me down a rabbit hole I think I've managed to crack! But will have to wait for confirmation from the client on the history of the repair done in it!

What I think has happened is that when the laptop died the client took it to a repair shop who did one of the following!

1. Replaced the motherboard which was probably a Q5WVH LA-7912P which does have the RTD2132S, with the current motherboard which is Q5WV8 LA-8331P rev 1.0. which means that the display that is original is not compatible with the LA-8331P as it's not a eDP display...
2. The board is the original Q5WV8 LA-8331P rev 1.0. which doesn't have the RTD2132S, but the display was changed for a 40 pin LED LVDS backlit display instead of a 30 pin eDP display!

Those are the only two conclusions I have, this is why I think @mon2 is right, if the current MB doesn't have the RTD2132S then the display MUST be a 30 pin eDP display otherwise no picture! But both of my displays are 40 pin LVDS screens made prior 2015 and I do believe most laptops prior 2015 didn't use eDP! (I could be wrong..)

So what that means is either the motherboard was swapped or the display was swapped causing the incompatibility! As I can't really find a fault with the motherboard other than the fact the CPU on the Q5WV8 LA-8331P board doesn't have any voltage at pin 4 and subsequently, the line ends up at pin 8 on the LVDS connector with 0v. Here's a compilation of images to explain what I mean.

Now I could be wrong as hell but that is the only logical thing my brain can produce! I will wait for the confirmation from the client to see if they can find out what the previous repair was and what they swapped or changed...

Anyone wise enough to confirm my suspicion is more than welcome